#!/bin/sh
# Filename: gencert.sh
# Description: This script generates x509 server certificate (with all IPs in
#              SAN) signed by a self-signed CA.
# Version: 0.1 - 30 June 2018
# Author: Andrey Arapov <andrey.arapov@nixaid.com>
# License: GPLv3

ME=$(printf '%s\n' "${0##*/}")

print_help() {
  printf "[${ME}] HELP: I accept following arguments:
  --help     - show this message
  --cn       - certificate's CN name\t\t(MANDATORY)
  --key      - server key name\t\t\t(default: private.key)
  --cert     - server cert name\t\t\t(default: public.crt)
  --days     - server cert expiration in days\t(default: 365)
  --cakey    - CA key name\t\t\t(default: ca.key)
  --ca       - CA cert name\t\t\t(default: ca.crt)
  --cadays   - CA cert expiration in days\t(default: 3650)\n"
}

# A POSIX variable
OPTIND=1 # Reset in case getopts has been used previously in the shell.

# read arguments
opts=$(getopt \
    --longoptions "help,cn:,key:,cert:,days:,cakey:,ca:,cadays:," \
    --name "$(basename "$0")" \
    --options "" \
    -- "$@"
)

eval set --$opts

while [ $# -gt 0 ]; do
  case "$1" in
    --help)
      print_help;
      exit 0
      ;;

    --cn)
      ARG_CN=$2
      shift 2
      ;;

    --key)
      ARG_KEY=$2
      shift 2
      ;;

    --cert)
      ARG_CERT=$2
      shift 2
      ;;

    --days)
      ARG_DAYS=$2
      shift 2
      ;;

    --cakey)
      ARG_CAKEY=$2
      shift 2
      ;;

    --ca)
      ARG_CA=$2
      shift 2
      ;;

    --cadays)
      ARG_CADAYS=$2
      shift 2
      ;;

    *)
      break
      ;;
  esac
done

if [ -z "${ARG_CN}" ]; then
  echo "[${ME}] ERROR: Please specify CN, example \"--cn your.site.com\""
  print_help;
  exit 1
fi

# For debugging purposes
# echo ARG_CN=$ARG_CN
# echo ARG_KEY=$ARG_KEY
# echo ARG_CERT=$ARG_CERT
# echo ARG_DAYS=$ARG_DAYS
# echo ARG_CAKEY=$ARG_CAKEY
# echo ARG_CA=$ARG_CA
# echo ARG_CADAYS=$ARG_CADAYS

OPENSSL_CONFIG="openssl.cnf"
CA_KEY="${ARG_CAKEY:-ca.key}"
CA_CERT="${ARG_CA:-ca.crt}"
CA_DAYS="${ARG_CADAYS:-3650}"
SERVER_KEY="${ARG_KEY:-private.key}"
SERVER_CERT="${ARG_CERT:-public.crt}"
DAYS="${ARG_DAYS:-365}"

# set -x
set -e

gen_openssl_config() {
  OPENSSL_CONFIG_CONTENT="[ req ]
distinguished_name = req_distinguished_name
[req_distinguished_name]
[ v3_ca ]
basicConstraints = critical, CA:TRUE
keyUsage = critical, digitalSignature, keyEncipherment, keyCertSign
[ v3_req_server ]
basicConstraints = CA:FALSE
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
subjectAltName = @alt_names
[ alt_names ]"

  # Gather IPs for SAN
  
  i=1
  IPS="$(getent ahostsv4 $(hostname) | awk '{print $1}' |sort | uniq)"
  echo "[${ME}] Found these IPs: " ${IPS}
  PAYLOAD="$(for IP in $IPS; do echo "IP.${i} = ${IP}" ; i=$((i + 1)); done)"
  
  printf "${OPENSSL_CONFIG_CONTENT}\n${PAYLOAD}\n" > "${OPENSSL_CONFIG}"
}

gen_ca() {
  echo "[${ME}] Generating new CA: ${CA_KEY} / ${CA_CERT} ..."
  openssl ecparam -name prime256v1 -genkey -noout -out "${CA_KEY}"
  chmod 0600 "${CA_KEY}"
  openssl req -x509 -new -sha256 -nodes -key "${CA_KEY}" -days "${CA_DAYS}" -out "${CA_CERT}" \
              -subj "/CN=my-CA"  -extensions v3_ca -config "${OPENSSL_CONFIG}"
}

gen_server_x509() {
  echo "[${ME}] Generating new server x509: ${SERVER_KEY} / ${SERVER_CERT} ..."
  openssl ecparam -name prime256v1 -genkey -noout -out "${SERVER_KEY}"
  chmod 0600 "${SERVER_KEY}"
  openssl req -new -sha256 -key "${SERVER_KEY}" -subj "/CN=${ARG_CN}" \
    | openssl x509 -req -sha256 -CA "${CA_CERT}" -CAkey "${CA_KEY}" -CAcreateserial \
                   -out ${SERVER_CERT} -days "${DAYS}" \
                   -extensions v3_req_server -extfile "${OPENSSL_CONFIG}"
}

install_openssl() {
  set +e
  type openssl >/dev/null 2>&1
  if [ $? -eq 0 ]; then
    return;
  fi

  if [ -f /etc/debian_version ]; then
    echo "[${ME}] Installing openssl in Debian/Ubuntu"
    export DEBIAN_FRONTEND=noninteractive
    apt-get update
    apt-get -y install openssl
  elif [ -f /etc/alpine-release ]; then
    echo "[${ME}] Installing openssl in Alpine"
    apk add --update openssl
  elif [ -f /etc/centos-release ]; then
    echo "[${ME}] Installing openssl in CentOS"
    yum -y install openssl
  fi

  type openssl >/dev/null
  if [ $? -ne 0 ]; then
    echo "[${ME}] ERROR: Could not install openssl. Exitting."
    exit 1
  fi
  set -e
}

start() {
  echo "[${ME}] Started in ${PWD} directory."

  install_openssl;
  gen_openssl_config;
  
  if [ ! -f "${CA_KEY}" ]; then
    echo "[${ME}] Could not find ${CA_KEY} file so I will generate a new one."
    gen_ca;
  fi
  
  openssl x509 -in "${CA_CERT}" -noout -checkend 2592000 >/dev/null
  if [ $? -ne 0 ]; then
    echo "[${ME}] WARNING! Your CA certificate will expire in less than 30 days."
  fi
  
  openssl x509 -in "${CA_CERT}" -noout -checkend 1 >/dev/null
  if [ $? -ne 0 ]; then
    echo "[${ME}] WARNING! Your CA certificate has expired, so we will generate a new one."
    gen_ca;
  fi
  
  # Generate a new server certificate with the detected IPs.
  gen_server_x509;
  
  echo "[${ME}] The certificates have been generated in ${PWD} directory."

  CERT_INFO="$(openssl x509 -in "${SERVER_CERT}" -noout -text)"
  echo "${CERT_INFO}" | grep -E "CN=|IP Address|Not\ "
}

start;